1. Field of the Invention
The present invention relates to the field of fuel injectors and more specifically, to fuel injectors having a nozzle with improved cooling.
2. Description of Related Art
Fuel injectors have been commonly used with internal combustion engines such as diesel engines to deliver combustible fuel to the combustion chambers within the cylinders of the engine. Various injector designs have been implemented in the art but most fuel injectors have a nozzle with a valve element movably disposed therein in which when opened, provides a spray of fuel into the combustion chamber of the cylinder. In this regard, fuel injectors typically include a nozzle including an outer barrel, a retainer, and a nozzle housing that houses the valve element of the fuel injector. The fuel injector is typically mounted to an injector bore in the cylinder head of the internal combustion engine and the nozzle housing having an injection hole generally extends at least partially into the combustion chamber so that fuel may be provided therethrough. In this regard, the retainer is received within the injector bores of the cylinder head and includes an opening proximate to the combustion chamber of the cylinder which allows the nozzle housing to extend into the combustion chamber. Such nozzle designs are generally illustrated in U.S. Pat. No. 5,441,027 to Buchanan et al.
The injector holes are typically provided at the tip of the nozzle shank of the nozzle housing and can be exposed to high temperatures in the combustion chamber of the cylinder during engine operation. It is not uncommon for flame temperatures in the combustion chamber to exceed 4000° Fahrenheit. Generally in the process of normal fuel injection, the fuel itself serves as a media which cools the injector and the tip of the nozzle shank as the pressurized fuel is sprayed from the injector hole. In addition, further cooling of the injector has been obtained by providing a water jacket around the fuel injector in which a cooling medium (such as engine coolant) is circulated to reduce the injector temperature. In this regard, a cost effective solution is to provide coolant passages open to the injector bore within the cylinder head, and to form a water jacket by inserting a coolant jacket sleeve made of copper or stainless steel into the injector bore to thereby segregate the coolant jacket from the injector. Thus, in this manner, efficient reduction in injector temperature has been readily attained and is currently used in many internal combustion engine applications.
More recently however, there has been a tremendous push to increase fuel efficiencies and reduce emissions in internal combustion engines, and in particular, in diesel engines. In a quest to attain these goals in which the injectors and the fuel systems operation must be optimized, engineers have utilized the fuel injectors to provide reduced injection flows such as in pilot injection, preinjection, and/or through the use of a second injector. In many such applications, the quantity of fuel injected is relatively small (less than 5 mm3/stroke). The present applicants have found that the cooling provided by the fuel flowing through the injector and being sprayed is insufficient to cool the tip of the nozzle. In such situations, the tip of the nozzle shank can experience temperatures in excess of its tempering temperature which is commonly approximately 450° Fahrenheit. Consequently, heat deformation of the nozzle tip and fuel coking have been identified by the present applicants as a direct result of insufficient cooling. Moreover, with the advent of increased emissions regulations, alternative fuels and blends thereof have been pursued to provide alternative combustible fuels that may be used in various internal combustion engines such as modified diesel engines. However, such alternative fuels have different burn temperatures and characteristics, and certain fuels such as natural gas has a tendency to burn with a combustion flame which is positioned closer to the tip of the nozzle thereby exposing the tip of the nozzle to much higher temperatures than those experienced during normal diesel fuel combustion.
In addition to the above described method for reducing injector temperature by providing water jackets around the injector, there have been various devices and methods proposed for reducing the temperature of the tip of the nozzle tip during operation of the internal combustion engine. In particular, the Australian Patent No. 204195 discloses an injector including a joint tightening cone with a central opening to receive the nozzle housing therethrough. This reference discloses that the cone is made of a different material than the nozzle and is made of material having good heat conduction such as aluminum or copper. During operation of the internal combustion engine, the cone expands to tightly contact the nozzle shank of the nozzle housing thereby preventing heating of the nozzle tip that may be caused by entrance of combustion gases at the interface of the cone and the nozzle shank. The reference further discloses that a very favorable heat transmission conditions from the nozzle tip to the cooled cylinder head is provided via the cone. The disadvantage of the invention disclosed in this reference is that it requires a cone having a different material composition than the rest of the injector which may increase manufacturing costs and further complicate the operation of the injector due to the differing expansion and contraction characteristics of the cone as compared to various other components of the injector. In another approach, U.S. Pat. No. 5,860,394 discloses an injector having a nozzle tip which has an approximately 45° angle tapered nozzle tip surface which abuts a heat insulator that reduces the heat conducted from the cylinder head to the injector tip and further serves as a seal against the coolant flowing around the injector. The disadvantage of this design is that it is highly sensitive to manufacturing tolerance variances and is susceptible to failure due to the reduced material thickness of the cylinder head caused by the coolant passage that must flow very close to the nozzle tip.
Therefore, there exists an unfulfilled need for an improved fuel injector having a nozzle with improved cooling. In particular, there exists an unfulfilled need for such a nozzle that will increase reliability and performance of the fuel injector. In this regard, there is an unfulfilled need for such a nozzle which is sealed to prevent entry of combustion gases to thereby prevent heat transfer from the combustion gases to the nozzle without the disadvantages of the prior art designs, especially when the fuel injector is used for pilot injections or used with alternative fuels.